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I have a table created like this originally:
CREATE TABLE dbo.XX ( YY int DEFAULT(NULL) ) If you do this, and then script the table later on, you will get the following code, plus a randomly named default constraint:
CREATE TABLE [dbo].XX([YY] [int] NULL) GO ALTER TABLE [dbo].XX ADD DEFAULT (NULL) FOR [YY] GO Now is there any real point in specifying DEFAULT (NULL) on a column instead of just leaving it as [YY] [int] NULL in the first place?
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No, it isn't necessary because without adding DEFAULT NULL, it gives NULL value. For example, let's say you haven't added DEFAULT NULL and inserted a record with no value, then the result would display the NULL value as the inserted value.
The Simple AnswerIf the column is nullable then it will create the column with a NULL value instead of the default value, however, if column is not nullable and there is a default value, SQL Server has to apply that value to column to avoid violating not null constraint.
If a data type specification includes no explicit DEFAULT value, MySQL determines the default value as follows: If the column can take NULL as a value, the column is defined with an explicit DEFAULT NULL clause. If the column cannot take NULL as a value, MySQL defines the column with no explicit DEFAULT clause.
By default, a column can hold NULL values. The NOT NULL constraint enforces a column to NOT accept NULL values. This enforces a field to always contain a value, which means that you cannot insert a new record, or update a record without adding a value to this field.
There is no need to add a DEFAULT(NULL) to nullable columns.
If data is not supplied to such columns, they will have a NULL.
The only benefit I see is the one Larry Lustig has posted in his comment to the question - it documents the fact that you have not forgotten to add a default to the nullable column.
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